The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 100 10 772.9, filed on Mar. 4, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a calender with a stand, an upper roll, a lower roll, and two center rolls located between the upper and lower rolls. The two center rolls are supported on the stand by way of cylinders.
2. Discussion of Background Information
A calender similar in general to that discussed above is known from DE 37 02 245 A1. Further, U.S. Pat. Nos. 4,736,678 and 5,806,415 disclose similar type calenders as well.
Cylinders, which can also be referred to as, e.g., compensation cylinders, are either directly or indirectly supported on the stand or frame of the calender. Further, the cylinders are utilized for different purposes, e.g., during operation, when a material web is glazed, the cylinders compensate for overhanging loads on the roll, e.g., guide rolls or scrapers, or a part of the roll load itself. In a calender according to, e.g., U.S. Pat. No. 5,806,415, even the entire roll weight is compensated by these cylinders. The advantages resulting from this operational mode are more even line loads across the width and higher line loads being possible in the upper nips while maintaining even line loads in the lower nip.
A second purpose of the cylinder is to allow a quick separation of the rolls, i.e., opening the nips as abruptly as possible. Such an opening is necessary in certain situations of malfunctions, e.g., a web break, to avoid damage to the rolls.
Such quick separations are known per se. For this purpose, the lower roll is dropped and the cylinders of the center rolls are relaxed. In order to avoid a hard impact of the rolls, dampening is provided for the final position, i.e., at the end of the piston motion of the cylinders, the cross section for the hydraulic fluid to discharge is reduced so that the roll is slowed more gently to some extent at the end of its motion.
The present invention is directed to improving the quick separation capabilities of the calender.
According to the invention, a calender of the type mentioned at the outset is provided with a discharge path controlled over more than xc2xe of a piston stroke necessary for lowering the center roll.
Further, it is noted that the instant invention is described, by way of example, as a calender in which the center rolls are positioned on the stand by way of levers. However, it is noted that this is purely for the purpose of explanation and illustration, and that other arrangements are likewise contemplated, e.g., positioning the rolls in linear guides.
In accordance with the features of the instant invention, the abilities of control are no longer limited to braking the roll at the end of its motion, which ultimately has the effect of avoiding an abrupt contact of the roll and the shock connected therewith. Moreover, it is possible to control the roll throughout the longest part of its motion. Thus, it is now possible to increase the speed of lowering the rolls and opening the nips. Relatively high motion speeds can be permitted, especially at the beginning of the motion. Additionally, it is now possible to adjust the motion of neighboring rolls to one another so that, during the opening motion, a collision of neighboring rolls can virtually be excluded.
Preferably, the discharge path is controlled by a motion of the piston in relation to the cylinder housing. This results in the control by the motion of the roll itself. External measures are not necessary, so additional control mechanisms can be omitted.
Preferably, the resistance of the discharge path increases the farther the piston is inserted into the cylinder housing. This applies for the usual procedure in which the nips are closed when the piston is extended. In cases in which the nips are closed by a cylinder operating in reverse, the resistance of the discharge path increases accordingly. With such a design, the motion speed of the center roll can be controlled so that the opening motion can be introduced very quickly, but can then be decelerated increasingly. Thus, the entire opening motion requires the same amount of time as in known cases. However, the increase of the nip opening at the beginning of the motion occurs more quickly.
Preferably, the cylinders of different center rolls are provided with different resistances of discharge paths in the case of closed nips, with the resistance increasing from the bottom to the top. This takes into account the fact that the uppermost center roll must travel a shorter total distance than the lowermost center roll. Essentially, the uppermost center roll has to travel only the distance that corresponds to the desired nip opening. The subsequent center roll must already travel a distance twice as long, i.e., the distance necessary for opening the nip between the uppermost and the subsequent center roll by the predetermined amount plus the opening width of the uppermost roll. In order to avoid a collision of the xe2x80x9cfallingxe2x80x9d rolls the resistance of the discharge path is selected such that the uppermost roll falls more slowly and the initial speeds of the rolls during opening increases from the top to the bottom. This can be performed easily by already providing different resistances in the discharge paths before the beginning of the motion of the rolls. The roll with the lowest resistance in the discharge path can remove the hydraulic fluid from the piston the fastest and, therefore, travel a longer distance during the same time.
Preferably, the pistons are embodied identically to one another, but the pistons are extended to different lengths when the nips are closed. When the distance in the discharge paths is dependent on the position of the piston, the relatively simple possibility results of providing different flow resistances for different roll positions in spite of identical pistons. When the piston is inserted farther, the discharge path already has a greater resistance. Such a piston inserted farther can be found in a roll positioned further up. The lowermost center roll has the piston that is pulled out the farthest and, thus, the lowest discharge resistance in the discharge path.
Advantageously, a pipe is provided in the cylinder housing, having openings in its wall and protruding into a bore of the piston. This pipe forms the variable resistances in the discharge path of the cylinder. The more free openings in the wall of the pipe, the smaller the resistance in the discharge path. When the piston is being driven in, more and more openings in the wall of the pipe are covered and, thus, the resistance in the discharge path is automatically increased.
Preferably, the pipe extends into the piston over the entire piston stroke. This allows a speed control over the entire piston stroke. The pipe is guided over the entire piston stroke in the piston and, thus, fixed so that possibility of error remains small.
Preferably, a seal is provided between the piston and the pipe. This creates clearly defined flow relations. Moreover, hydraulic fluid is prevented from seeping through a gap between the piston and the pipe and, thus, from resulting in uncontrolled flow relations.
Preferably, the pipe is open at its face. This is of lesser importance for the lowering motion, i.e., the opening of the nips. However, this opening can be advantageous during closing, i.e., the hydraulic fluid in the interior of the piston can act in a supporting manner so that the piston can be driven out faster.
Advantageously, the pipe is centrally positioned in the cylinder housing and centrally in relation to the piston. In this way, unsymmetrical stress can be omitted.
In one embodiment it may be preferred for the openings to be evenly distributed over the length of the pipe. This can be achieved, e.g., by sizing all openings equally and by positioning them in the longitudinal direction in equal intervals. It is certainly possible as well to distribute several openings in the same xe2x80x9caltitudexe2x80x9d around the circumference of the pipe. When the piston is inserted into the cylinder housing, it covers a linearly growing opening area and thus reduces the discharge cross section. Naturally, due to the discrete distribution of the openings, this occurs discontinuously, which is of lesser importance. Such a linear behavior can be created by distributing differently sized openings in varying intervals over the length of the pipe. A linear deceleration per se can be achieved using such linear behavior.
In an alternative embodiment, provisions is made for the openings to be distributed over the length of the pipe according to a predetermined non-linear function, with the discharge cross section shrinking disproportionally at the end of the lifting motion. Therefore, the discharge cross section is still the smallest at the end of the lifting motion. However, the increase of the cross section during the exiting of the piston or the reduction of the cross section during the insertion of the piston does not occur linearly, but rather according to another function, preferably a quadratic function. Thus, it is possible to provide a far larger discharge cross section at the beginning of the piston motion, which allows a faster piston movement, while the piston is decelerated more towards the end of the motion.
Preferably, the discharge path is connected to a control device which prevents the pressure in the piston from dropping. When all nips are closed, the center rolls are at least partially supported by the rolls positioned underneath. The cylinders accept some of the load, which is expressed in a corresponding pressure in the cylinders. When the support of the lower rolls is gone, the pressure in the cylinder rises accordingly. The control device ensures that the hydraulic fluid cannot exit the cylinder. However, it also ensures that the pressure in the cylinder does not drop, i.e., that the roll remains held by a certain force. The lowering motion can be controlled well in this manner so that a collision of rolls can be avoided.
In a preferred embodiment, it is even provided for the control device to slightly increase the pressure in the cylinder during the insertion of the piston. This improves the xe2x80x9cdeceleration behaviorxe2x80x9d at the end of the motion. Only when the roll has reached its xe2x80x9cfinal positionxe2x80x9d at which the appropriate nips are completely open the pressure is released. In this case, the roll or the lever can rest on a final contact, for instance.
The present invention is directed to a calender that includes a stand, an upper roll, a lower roll, and at least two center rolls arranged between the upper and the lower rolls. The calender also includes at least two cylinders, where the at least two center rolls are supported on the stand by the at least two cylinders. Each of the at least two cylinders include a discharge path that is controlled over more than xc2xe of a piston stroke for lowering the at least two center rolls.
In accordance with a feature of the present invention, each the at least two cylinders can include a piston and a cylinder housing. The discharge path may be controlled by movement of the piston in relation to the cylinder housing.
According to another feature of the invention, a resistance of the discharge path can increase as the piston slides farther into the cylinder housing.
Moreover, each of the at least two cylinders can be assigned to different ones of the at least two center rolls, and the upper roll, the at least two center rolls, and the lower roll may be arranged to form a roll stack. Each cylinder can be structured and arranged to have different resistances in the discharge paths, and the at least two cylinders may be arranged so that the resistance in the discharge path increases from a bottom of the roll stack to a top of the roll stack. The pistons of each of the at least two cylinders may be structurally the same. When the upper roll, the at least two center rolls, and the lower roll are arranged to close the nips between adjacent rolls, each piston can extend from an associated cylinder to a different degree. When the nips are closed, each piston may extend a different distance from the associated cylinder. Further, the distance that each piston extends from the associated cylinder can increase from a bottom of the roll stack to a top of the roll stack.
Each of the at least two cylinders may include a cylinder housing and a piston with a bore, and the calender can further include a pipe located inside the cylinder housing comprising a wall and openings formed through the wall. The pipe may be arranged to extend into the bore. The pipe can slidably extend into the piston over the piston stroke. Further, a seal may be positioned between the piston and the pipe. The pipe can be open on its face. Still further, the pipe may be centrally located in the cylinder housing and centrally in relation to the piston. Moreover, the openings can be evenly distributed over a length of the pipe. Alternatively, the openings can be distributed over a length of the pipe in accordance with a predetermined non-linear function, such that a discharge cross-section shrinks disproportionally at an end of a lifting motion. The predetermined non-linear function may include a quadratic function.
In accordance with still another feature of the invention, each of the at least two cylinders can include a cylinder housing, and the calender may further include a control device coupled to the discharge path to prevent a decrease of pressure in the cylinder housing. Each of the at least two cylinders may further include a piston, and the control device can be structured and arranged to slightly increase pressure in the cylinder during insertion of the piston.
The present invention is directed to a process of quick releasing nips in a calender that includes a stand, an upper roll, a lower roll, at least two center rolls arranged between the upper and the lower rolls, at least two cylinders arranged to support the at least two center rolls on the stand, where each of the cylinders include a discharge path. The process includes lowering the lower roll away, whereby closed nips between adjacent rolls are opened, and, during opening of the nips, controlling a discharge path of the cylinders supporting the at least two center rolls over more than xc2xe of a piston stroke for lowering the at least two center rolls.
According to a feature of the instant invention, each of the at least two cylinders can include a piston and a cylinder housing, and the discharge path can be controlled by movement of the piston in the cylinder housing.
In accordance with another feature of the invention, each of the at least two cylinders can include a piston and a cylinder housing, and a resistance of the discharge path may increase as the piston slides into the cylinder housing.
Further, each cylinder can be structurally identical, and a distance traveled by each piston during the opening of the nips may be different.
The present invention is directed to a calender that includes a roll stack including a plurality of rolls, and the plurality of rolls includes an upper roll, a lower roll, and at least two center rolls located between the upper roll and the lower roll. Compensation cylinders are provided, each compensation cylinder including a piston and a cylinder housing. At least one compensation cylinder can be associated with each at least two center rolls. Each compensation cylinder can further include a pipe slidably extendable into the piston, the pipe having a wall and a plurality of through holes arranged over a length of the pipe.
In accordance with a feature of the invention, the pipe can be coupled to the cylinder housing.
In accordance with yet another feature of the instant invention, a pressure chamber may be formed between the piston and the cylinder housing which is filled with hydraulic fluid. The hydraulic fluid may exit the pressure chamber through the through holes and the pipe. Further, as the piston slides into the cylinder housing, a resistance of a flow of the hydraulic fluid in a pressure chamber may be increased due to a reduced number of through holes in the pipe.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.